This project is for the development of a system for direct scanning of gel filtration columns. We use a JY Optics monochromator as a source of light providing a collimated beam of a particular wavelength under computer control. The beam is split by a quartz plate so that part of its passes to reference photomultiplier. The remainder is reflected from a front silvered mirror through a chromatography column with appropriate slits interposed to give resolutions of lmm. The signals received by the reference and sample photomultiplier are combined in a log ratio operational amplifier to give an output which is the absorbancy of the column plus solute. This signal is converted for digital processing by a PDP1104 minicomputer. Output is to either a video monitor or an X-Y recorder under control of the computer. The system is to be applied to studies of interaction between proteins. We plan to investigate specifically the interaction of nitrogenase components, cytochrome c with cytochrome oxidase, and other systems which have visible spectral components.